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How do I descale/flush the heat exchanger

Descaling and flushing your tankless water heater for proper maintenance.

If you live in an area with hard water but do not have a water softening system or a Noritz anti-scale treatment device, you will need to descale the unit periodically based on the guidelines in the manual.

In the owners and installation manual of your unit you will find charts similar to these below.

Flushing or De-scaling is part of the regular maintenance of a Noritz heater.  It involves circulating a solution of pure vinegar or Calcium, Lime, and Rust product through the heat exchanger using a submersible pump.  You will need the following equipment to conduct a de-scale:

  • Bucket 
  • Submersible pump 
  • Isolator valve kit (installed on heater) 
  • Water line connections (the isolator valves have a 3/4″ hose thread connections on their flush ports)
  • Descaling solution (vinegar or Calcium, Lime, Rust product)

For complete step by step instructions, please see the attached instruction manual.

For units that start with the following names below, see attached file “Descale Procedure Group A Zone II”.

• NR501-OD

• NR662-OD

• NRC661A-OD

• NRC661A-DV

• NRC711-OD

• NRC711-DV

• NRC663-FSV (EZTR40)

For units that start with the following names below, see attached file “Descale Procedure Group B Zone III”.

• (GQ-2457….)

• (GQ-2857….)

• (GQ-C2857…)

• (GQ-C3257…)

For units that start with the following names below, see attached file “Descale Procedure NRCB180 NRCB199”.

• NRCB199DV (GHQ-C3201WX-FF US)

• NRCB180DV (GHQ-C2801WX-FF US)

For all other units not listed above, see attached file “Descale Procedure Group C”.

For a general outline of how to descale, please check out this video:

Updated on July 30, 2021

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